Probability analysis of system special operation mode in the lightning invasion over-voltage calculation of UHV AC Substation

The international standard IEEE p1862-2014, IEEE recommended practices for overvoltage and insulation coordination of transmission system at 1000kV AC and above, and the Chinese national standard GB/Z 24842–2018, overvoltage and insulation coordination of 1000kV UHV AC transmission and transformation engineering, clearly stipulate as follows. For UHV AC substation, normal operation mode and special operation mode should be considered in the calculation of lightning over-voltage in substation. The normal operation mode is generally considered as follows. For 330kV, 500kV and 750kV EHV transmission system, N-2 (N is the number of outgoing circuits) is the most severe mode due to its large number of outgoing circuits and a large number of safe operation experience. For 1000kV UHV transmission system, considering the importance of UHV substation, single line and single transformer mode is the most severe mode of general operation. Special mode is the operation mode of the substation line breaker in the open circuit state. The possible causes of special ways are lightning stroke before line closing, lightning stroke before reclosing after line tripping, and lightning stroke before line connection. The overvoltage is more serious, but it is less likely to occur. The probability of the above situations should be considered in the prediction of overvoltage. This paper focused on the analysis of the special operation mode that the circuit breaker of the substation was in the open circuit state. This paper studied the probability of three main special operation modes before line closing, before line trip, before reclosing and before line grid connection, and finally obtained the total probability of special operation mode, and the calculation method of safe operation year of substation considering the total probability of special operation mode. The research results refined the standard provisions of IEEE P1862-2014 and GB/Z 24842–2018, improved the enforceability of the standard, and greatly improved the reliability of lightning protection and operation safety of UHV AC substation.